Screw-cutting tool



(No Model.)

P, G.-EOHOLS. SCREW CUTTING TOOL.

No. 588,056. Patented Aug. 10,1897.

Invent??? flank (Z Echols 33 7a attorney UNITED STATES PATENT OFFICE.

FRANK G. ECHOLS, OF HARTFORD, CONNECTICUT.

SCREW-CUTTING TOOL.

SPECIFICATION forming part of Letters Patent No. 588,056, dated August10, 1897.

Application filed May 8, 1897. Serial No. 635,656. (No model.)

To all whom it may concern:

Be it known that I, FRANK Gr. ECHOLS, a citizen of the United States,residing in Hartford, in the county of Hartford and State ofConnecticut, have invented certain new and useful Improvements inScrew-Cutting Tools, of which the following is a specification.

This invention relates to improvements in screw-cutting tools, such astaps and dies, for forming internal and external screw-threads and ithas for its main object the provision of an improved tool of this typeby means of which screw-threads may be out easily and rapidly withoutbreaking or distorting the same and without injuring the tool used forthe purpose.

In screw-cutting tools heretofore employed, in which the teeth in agiven row are arranged consecutively, one tooth for each turn of thethread being cut, the row of teeth form together a complete wingextending transversely of the article being threaded, so as to. carryforward with the row of cutting faces or teeth not only the chips formedthereby, but also the lubricating material, thereby wiping offsubstantially all of the lubricating material from the freshly-cutsurfaces and leaving only the clean metal in the path of succeedingcutting faces or teeth of the tool. In my improved tool, however, thereare formed in each wing thereof numerous blank spaces, through which thechips, and especially the lubricating material, may. pass freely aroundthe threading-tool while this is in use, the lubricating materialflowing around from one groove to another and thus lubricating thefreshly-cut surfaces immediately in advance of the cutting-teeth andwith a gradually-increased thoroughness and efficiency. In order toattain this result and form these blank spaces between the teeth of theseveral wings of the cutting-tool, I so dispose the cutting-faces thatthe centers of adjacent teeth will be spaced at greater intervals thanthe pitch of the thread to be cut, the preferred construction being onein which the teeth in each wing are separated by intervals which aremultiples of the pitch of said thread. Moreover, these teeth and thespaces therebetween are so located that some of the turns of the threadof the tool will have a less number of teeth than the number of wingsfrom which the teeth rise, the teeth and the blank spaces preferablyalternating in each turn.

In the construction illustrated in the drawings, which is the one Iprefer to employ, I have shown in each view a screw-cutting tool havingan odd number of wings formed with teeth and blank spaces, which arelocated in a single spiral and alternate from end to end thereof, sothat there will be a blank space in each wing between the precedingcuttingtooth in the wing in advance of that containing such blank spaceand the succeeding tooth in the wing in the rear of such blank space. Bymeans of this organization of the teeth of the threading-tool relativelyto the blank spaces thereof I am enabled to obtain the greatestefficiency and the best results, for the reason thatafter the tool hasstarted there will be a groove in the material oper- I ated upon betweeneach pair of teeth of the tool, and through this space the lubricant mayflow freely and the chips pass during the whole of the threadingoperation. Owing to the fact that this intermediate groove between twoadjacent teeth of the cutting-tool is always present after the threadingoperation has begun the threads at opposite sides of the groove arepermitted to yield sidewise toward each other, by reason of the mobilityof the material being cut, so as to facilitate materially the operationof the tool and prevent binding thereof.

It should be stated here that in my improved screw-cutting tool I amenabled to make use of cutting-teeth having no side relief whatever, asthere is always a suflicient space between each pair of adjacentcuttingteeth to permit this sidewise yielding of the screw-threads whenthe pressure of the sides of the cutting-teeth is applied thereto.

In the drawings accompanying and forming part of this specification,Figure 1 is a side elevation of a tap constructed in accordance with myimprovements. Fig. 2 is a transverse section of the same, the sectionbeing taken in the line 2 2, Fig. 1. Fig. 3 is a developed view of theperiphery of the cutting tool or tap shown in Fig. 1, this viewillustrating the manner in which the cuttingteeth and the blank spacesalternate. Fig. 4 is a sectional detail, on an enlarged scale, showingthe manner in which adjacent teeth too operate to cut the outer sides ofadjacent threads which have a clear space or groove between them and arefree to move toward each other. Fig. 5 is a plan of a modification of myinvention, showing a separable die and die-stock, in which the former isconstructed to operate in the same manner as the tap hereinbeforedescribed. Fig. 6 is a transverse section of the same, the section beingtaken in line 6 6, Fig. 5. Fig. 7 is a plan of a solid die alsoembodying my invention; and Fig. 8 is a transverse section of the same,taken in line 8 S, Fig. 7.

Similar characters designate like parts in all the figures of thedrawings.

As before stated, one of the main features of my invention consists inspacing adjacent cutting faces or teeth so that there will be a greaterinterval between the centers of those teeth than the pitch of the threadwhich is to be cut.

Preferably the cutting-teeth are disposed insuccessive rows or wings insuch a manner that some of the faces of one row are followed by a blankspace or spaces in the following row.

Referring first to Figs. 1 to 3, inclusive, T

. designates in a general way a tap, of taper construction, having fivewings, each designated by w. The cutting-teeth by means of which thescrew-thread is to be formed may be located in any manner within thescope of my invention so long as the-distance between the centers ofsome of the adjacent teeth of the tool is greater than the pitch of thethread to be cut thereby. In this case, however, the teeth, which areindicated by t, are formed in rows, one row for each wing 10, and areseparated by blank spaces or interdental spaces 8, the teeth and thespaces alternating from end to end of each wing. These interdentalspaces are at all points of the full depth of the teeth, havesubstantially flat bottom walls, and are preferably of such size thatthe teeth in each wing are spaced at intervals which are multiples ofthe pitch of the thread to be formed by the tool, the teeth in this casebeing disposed at intervals twice that of such pitch. This will be clearby reference to Figs. 1 and 3, and, moreover, it will be seen byreferring to Fig. 3 that the teeth and the interdental spaces alternatealso in the direceration a cutting-tooth will be succeeded by of the tapshown in these figures one cuttingtooth comes between two adjacent turnsof the thread, so as to cut theouter face or side of each thread. Theinner side of each thread shown clearly in Fig. 4, and no pressure isbrought to bear upon these inner faces at any point in the lengththereof while the outer faces thereof are being cut at corresponding ithas been customary to plane opposite sides of the thread at anyparticular point at the same time, and this action has usually resultedin distorting or breaking off the edge of the thread, especially whenthe material operated upon has been such as would not oppose muchresistance to the pressure exerted against it.

By means of my present invention the thread being formed is relieved ofthe excessive pressure due to the combined action of tool-cutting teethoperating simultaneously at opposite sides thereof, and is'therebyenabled to withstand the action of the tool, so that any number ofperfect threads may be formed easily in metals and under circumstancesin which threads have been made heretofore only with great difficultyand after the loss of a large percentage of the work and stock.

In Fig. 4 I have illustrated in detail, on an enlarged scale, the actionof two separated cutting-teeth upon two adjacent turns of the threadbeing cut thereby, thisview also illustratin g the intermediate groovewhich forms a flowage-space for distributing the lubricant, permittingthe escape of the chips and relieving pressure on the threads being cut.The material which is being threaded is represented here by B and may beassumed to be a nut.

4t 4 designate two adjacent threads which have been formedby the action.of the cutting-teeth, and 5 represents the groove between those threads.Y

The blank space between the teeth 2! tis indicated by 6 and is of thesame width as the mouth of the groove 5 in the material. One of theteeth 25 bears against the outer face of the thread 4. and the otheragainst the corresponding face of the thread 4; but as there is no toothof the tap between these threads at this point there is no pressure uponthe inner faces of the latter, and consequently the metal of the threads4 4 around the inner sides and at the extreme points of these threads isnot grasped between cutting-teeth, as would be the case if the threadswere formed by the ordinary tap.

It will be clear that no matter what the material of the stock may bethe base of each thread will exert a much greater resistance faces thegroove between these threads, as the material will be much better ableto maintain its shape and position when onlyone side thereof is cut at atime and the opposite side is free to yield during such cuttingoperation.

Another important advantage which I secure by my invention and one thatis due directly to the presence of this groove between adjacent turns ofthe thread is that very much less relief of the cutting-teeth may beused and that I may entirely dispense with the side relief for the sidesof the teeth. The result of this is to give the tool greater stabilityin action and render it more durable, thereby increasing the amount ofwork done by a tool of a given size and reducing the cost of such work.By thus overcoming the necessity for relieving the sides of the teeth Iam enabled to sharpen the cutting-faces indefinitely by grinding thecutting ends of the same, so as to keep the teeth perfectly sharpwithout changing the cross-sectional areaor form thereof.

It is well known that in ordinary practice the cutting-teeth cannot beground away on their faces to any considerable distance withoutaffecting materially the size of the threads produced by thecutting-tool.

By making the cutting-teeth of full width from the front to the rearedge thereof the tool can be turned backward freely without drawingchips between the rear ends of the teeth and the work, which wouldresult in binding the tool. Such binding is common in taps and dies,especially in hand-taps, and is the cause of much difficulty in thecutting of threads in many kinds of work, resulting frequently inserious injury to the thread and sometimes in tearing it entirely away.

It is particularly to be noted that the edges of the flat bottom wallsof the interdental spaces 6 act as knives and shave off the top of thethread as the tap is driven through the article to be threaded, andthereby remove any metal that may have been distorted or crowded out ofplace owing to the mobility of the metal in the thread-formingoperation.

In Figs. 5 to 8, inclusive, I have illustrated my invention inconnection with screw-cutting dies, Figs. 5 and 6 illustrating aseparable or expanding die and Figs. 7 and S a solid die.

In Figs. 5 and 6 the cutters 0 correspond to the wings 20, (shown inFigs. 1 to 4,) andthe cutting-teeth t alternate with blank spaces 5 ineach cutter, the teeth and the spaces also alternating in the directionof the thread.

In Figs. 7 and 8 the wings w correspond to the wings 10, (shown in Figs.1 to 4,) and the teeth t are similar to those shown att; but both theteeth t and the teeth 15" have concave faces instead of convex ones, asis the case with the teeth 25. In this solid die the teeth t and spaces8 alternate with each other in each wing and also in the direction ofthe spiral or thread in which they are located, the construction inthese views and in Figs. 5 and 6 being similar in every respect to thatillustrated in Figs. 1 to 4:, except that the dies are adapted to cutexternal threads and the taps internal threads.

Screw-cutting tools, both in the form of dies and in the form of taps,made according to this invention are found to operate with very muchless power than is required for screw-cutting tools of the old kinds;and I have also found that screw-cutting taps, especially such as areused for tapping nuts and for similar work, may be made much shorterthan they are ordinarily, while securing freer action, requirin g lesspower, and having greater durability, as indicated by a number of testsof the invention with tools of a variety of sizes and kinds. I

Having described my invention, I claim-- 1. A screw-cutting tool havingan odd number of wings each equipped with teeth having no side reliefand interdental spaces located in a single spiral and alternating fromend to end of the working portion of the tool, said interdental spacesbeing at all points of the full depth of the teeth and having flatbottom walls in line with the roots of said teeth.

2. A screw-cutting tap having an odd number of wings formed with teetheach of full width from the front to the rear edge thereof, andinterdental, spaces located in a single spiral and alternating from endto end' of the working portion of the tool, said teeth having no siderelief, and said interdental spaces being at all'points of the fulldepth of the teeth and having fiat bottom walls, substantially as andfor the purpose specified.

FRANK G. EOHOLS.

. IVitnesses:

FRED. J. DOLE, HENRY BISSELL.

